Alan Barr University of Oxford DMUH, July 2011 LHC (ATLAS) Dark Matter S EARCHES : U NCERTAINTIES.
Dark Matter and Sparticles at the LHCconferences.fnal.gov/dmwksp/Talks/schmitt.pdf · events / s...
Transcript of Dark Matter and Sparticles at the LHCconferences.fnal.gov/dmwksp/Talks/schmitt.pdf · events / s...
Dark Matter and SparticlesDark Matter and Sparticlesat the LHCat the LHC
The Hunt for Dark MatterSymposium at Fermilab
May 12, 2007
Michael SchmittNorthwestern University
1Dark Matter and Sparticles at the LHC
2Dark Matter and Sparticles at the LHC
The TEVATRON has discovered (so far)....
the top quark(Bs oscillations)
The LHC will discover (perhaps)...
the Higgs bosonsupersymmetric particlesKaluzaKlein states
DARK MATTER ??optimism abounds...
3Dark Matter and Sparticles at the LHC
Let's compare to the TEVATRON collider:p psee talk byJane Nachtman
TEVATRON LHC beams ppbar ppcircumference 6 km 27 kmenergy 2 TeV 14 TeVluminosity 1032 1034 cms
8 fb 300 fb
bunch spacing 392 ns 25 nscollisions/xing 6 20collab'n size 600 each 2000 eachrunning mo/yr 12 6
What is the LHC ?What is the LHC ?
LHC
4Dark Matter and Sparticles at the LHC
What is the LHC ?What is the LHC ?approximate event rates for 2 1033 cm2 s1
(which would give 20 fb1 in one year)
W e 40 4 108
Z ee 4 4 107
tt tbar 1.6 1.6 107
b bbar 106 1013
QCD jets (ET > 200 GeV) 102 109
gluino pairs (1 TeV) 0.002 104
Higgs (120 GeV) 0.08 8 105
events / s events/year
5Dark Matter and Sparticles at the LHC
LHC Running PlanLHC Running Plan
2007
2008
cooldown of LHC magnets proceeding nicely so far
planned engineering run at 980 GeV is now unlikely
failed quadrupole magnet – insitu repair seems possible
CMS and ATLAS will close up in November for CR's
14 TeV run planned for mid2008
aiming for a delivered luminosity of about 1 fb
CMS and ATLAS both will be ready for collision data
first calibrations & alignment to be done with 100 pb
6Dark Matter and Sparticles at the LHC
Cooling Sector 78
slightly below 2o K
1/8 of the complete LHC ring
3.3 km long – world's largest superconducting installation
200 dipoles arranged in 30 cooling cells
day 0
day 4
7Dark Matter and Sparticles at the LHC
LHC Detectors / CollaborationsLHC Detectors / Collaborations
ATLAS
8Dark Matter and Sparticles at the LHC
9Dark Matter and Sparticles at the LHC
Dark Matter at CollidersDark Matter at Colliders“Dark Matter feels very close” Pier Oddone“The LHC will be a Dark Matter factory.” Bob McElrath
Apparently we should just run the LHC (+ILC).....
All evidence for Dark Matter is purely gravitational.paradoxical that particle accelerator experimentscan tell you anything about this.
(Dan Bauer)
The key is Ted Baltz's “happy coincidence”(assume dark matter is particulate),take TeV or EWKscale masses,take coupling constants of order 1,you get the right annihilation crosssection.
a.k.a. the “WIMP Miracle” Jonathan Feng
10Dark Matter and Sparticles at the LHC
DM (particle) paradigmDM (particle) paradigmdark matter particles are weaklyinteracting
for sure no electric charge and no color,and we hope that they will oblige us with weak interactions
they are massivehappy coincidence argument: 50 – 5000 GeVthey could be much lighter or heavier, if we forget particle physics
there is only one type of dark matterand it can be produced directly or in “simple” cascades
there exists an efficient annihilation channelneeded to obtain the observed relic densityimplies the existence of another particle
simple composition?
11Dark Matter and Sparticles at the LHC
Bridging Colliders to the UniverseBridging Colliders to the Universe
If the particle physics prejudices are correct, new particlesare likely to be observed at the LHC.There may be evidence of massive, weaklyinteracting, neutral particles.This would support a particlephysics explanation for dark matter.
Can we go from there to validating this paradigm?obviously, identify the LHCWIMP and measure its propertiesessential to identify the particle(s) responsible for annihilationcannot prove longterm stability, socorroboration with directdetection experiments is essential.don't know local dark matter density, so indirectdetection neededto tie directdetection + collider information to astrophysics data
Colliders provide the means to measure particle properties, and one of these particles may turn out to be the dark matter particle.
12Dark Matter and Sparticles at the LHC
LHC: testing the paradigmLHC: testing the paradigmFocus will not be on calculating relic densities...
several studies show this is unlikely / very difficult – needs an ILC
Can the LHC rule out the standard paradigm?there should be a missing energy signal from particle X!more interesting: can we find the particle Y participating in annihilation?can we show that the mass difference MY – MX is appropriate?to what extent can we test the properties of X and Y?
Can the LHC fail to observe dark matter particles?yes, if it were very light or very heavymoreover, we could fail to find particle Y
example: Higgs decays invisibly or to jetssee talk by Carlos Wagner
13Dark Matter and Sparticles at the LHC
be optimistic & hopefulbe optimistic & hopeful
Despite these caveats, suppose this particle physics paradigm is true.
Or more conservatively, suppose there is no immediate “no” answer.
How can we make progress toward confirming this picture?
14Dark Matter and Sparticles at the LHC
Establish a Missing Energy SignalEstablish a Missing Energy Signal
Here's one !!!
Jane Nachtman
trileptons
15Dark Matter and Sparticles at the LHC
Jim Linnemann
Here's another one !!!
How do they do it ???
16Dark Matter and Sparticles at the LHC
Establish a Missing Energy SignalEstablish a Missing Energy Signal
How do we establish a genuine missing energy signal?
missing energy is an apparent azimuthal imbalance in calorimeter energy.many sources of fake missing energy
muonsenergy lost in uninstrumented regionssevere measurement errors (calorimetry, tracking)energy from unrelated processes (other interactions, cosmics)
neutrinos...resolution on MET determines the shape
how long are the tails ??must calibrate the rates of all sources of fake MET
17Dark Matter and Sparticles at the LHC
MET resolution is understood on basis of “SUMET”SUMET = straight sum of calorimeter energies
noise & stochastic termsimportant at low SUMET
constant term in calor'yresolution at high SUMET
resolution depends on eventtype due to differingparticle content
validate resolution usingsource of neutrinos:W's, Z's and top
(Z, remove muons)
18Dark Matter and Sparticles at the LHC
Backgrounds normalized by appropriate reference processes.CMS
important backgrounds:t tbardibosons WW, WZ, ZZZ + jetsmultijet QCD
normalize to similar processesexample: Z + jetssimilarly for t tbar
shape of multijet background (scary!)obtained from reference samples(release certain topological cuts)
19Dark Matter and Sparticles at the LHC
MET signals for 1 fb (1st year?)
light mass point (Mgluino = 600 GeV)
high mass point (Mgluino = 1 TeV)
20Dark Matter and Sparticles at the LHC
Measure Dark Matter Particle PropertiesMeasure Dark Matter Particle Properties
mass spin couplings
no general way to obtain the masscaveat: see interesting developmentsby Bob McElrath
no way to obtain spin and couplingsno branching ratios....
must infer these quantities indirectly,assume relations among “similar” particlesbefore we have data, case studies.
21Dark Matter and Sparticles at the LHC
One Model out of ManyOne Model out of Many
Elli
s et
al.,
Bae
r & T
ata,
for e
xam
ple
1
2
3
4
Identify several regions giving the right relic density (“WIMP Miracle”),distinguished by the method for efficient annihilation.
1) “bulk” 2) “coannihilation” 3) “focuspoint” 4) “funnel”light sfermions degeneracy w/ stau or stop gauge bosons CPodd Higgs
22Dark Matter and Sparticles at the LHC
““Easy” Point in the Bulk RegionEasy” Point in the Bulk Regionsquarks around 550 GeV, gluino around 600, neutralino at 96 GeV
g qL q qL2
0 q 20 lR l lR
10 l
reconstruct chain from bottom up, use kinematic features opportunistically
ask for 4 highET jets, larget MET and two oppositesign leptons (e or )
only serious background: ttbar, which gives e as often as ee+
dilepton invariant mass has a sharp edge:
depends on masses of two neutralinosand the (light) slepton mass
edge measured to a fraction of a GeV
talk about “miracles”
ATLAS 100 fb
LH
CIL
C study
start here end here
23Dark Matter and Sparticles at the LHC
CMS study
ATLAS TDR
One can reconstructsquark masses, and then gluino masses.
Make clever use of kinematicextremes, possible when eventsamples are very large.
does not give M
Even more clever – and complex – analysis.● use both min and max kinematic endpoints● crucial is min(l+lq) measurement● conclusion:
measure M to about 10% for 100 fb
This is a very special case study!In general, no direct measurement is possible.
24Dark Matter and Sparticles at the LHC
Other points are more difficult!Other points are more difficult!
coannihilation
funnel(s)
focuspoint
squarks and gluinos heavystaus impossible to findstops very challenging, but not impossible...
most important: pseudoscalar Higgs, Alikely to be found in or other channelsother sparticles difficult to analyze in detaildetailed, precise kinematic studies unlikely
few sparticles can be observedlepton branching ratios are smallneutralinos = mixed binohiggsino
25Dark Matter and Sparticles at the LHC
What are we hunting?What are we hunting?
hard & dangerous...
hard...
hard...
easy ?
26Dark Matter and Sparticles at the LHC
Find the “other” particleFind the “other” particleinteresting that Higgs sector is prominentin three out of four regions
we need to validate the annihilation processdirectly from collider data a.f.a. possible
perhaps understanding Higgs sector at LHCmore important than constraining severalSUSY parameters & calculating h2
“Easy” Higgs signal in A,H
27Dark Matter and Sparticles at the LHC
Higgs Bosons Bridge Colliders and Higgs Bosons Bridge Colliders and Directdetection experimentsDirectdetection experiments
nice interplay between, say, CDMS and Tevatron/LHCmixed binoHiggsino state is good for bothif one or the other does not see DM particles, interesting....
Carena, Hooper, Vallinotto (2007)
mA M M
tan
(N
)
(N
)
CDMS sees signal soon
TEVATRON sees a Higgs LHC sees Higgs(es)
“Easy” Higgs signal in A,H “Easy” Higgs signal in A,H
28Dark Matter and Sparticles at the LHC
hunting the Higgs bosonshunting the Higgs bosonsinteresting that Higgs sector is prominentin three out of four regions
we need to validate the annihilation processdirectly from collider data a.f.a. possible
perhaps understanding Higgs sector at LHCmore important than constraining severalSUSY parameters & calculating h2
● even more interesting: connection w/ baryogenesis
● light gauginos = a sitting duck?● watch out: invisible Higgses!!
see Carlos Wagner's talk
29Dark Matter and Sparticles at the LHC
Overall Mass ScalesOverall Mass Scales
M eff = ET1ET2ET3ET4MET correlates with SUSY mass scalehepph/9610544
SUSY
SM
The production of squarks and gluons should be so copious that the simplest possiblemeasure of “lots of energetic jets + MET” will already indicate SUSY mass scales.
This kind of inclusive measure will help us identify which region we are in.
30Dark Matter and Sparticles at the LHC
ConclusionConclusionThe LHC probably will not allow us to compute relic densities,
but it will certainly set us on the path to understanding dark matter.
Soon we will all be
on the hunt...
31Dark Matter and Sparticles at the LHC
Here's another one !!!
search for squarks and gluinos